There are over 50,000 free plugins in the WordPress.org Plugin Directory, and many more can be purchased from premium plugin vendors. Most websites built bespoke by agencies also make use of compatibility plugins, which add functionality, custom post types and custom forms for data input to the site. WordPress comes with two plugins packed-in: Akismet and Hello Dolly.
Plugins can be used for everything imaginable, but some of the more common usecases are contact form plugins, SEO plugins, e-commerce plugins and security plugins. Plugins are handled in the “Plugins” page in the administration panel. In Plugins → Add New, you can also explore and install plugins directly from the WordPress.org plugin directory.
The following is a list of some of the more notable plugins in the WordPress ecosystem: